A research synthesis was conducted to examine the relationship between a written emotional expression task and subsequent health. This writing task was found to lead to significantly improved health outcomes in healthy participants. Health was enhanced in 4 outcome types—reported physical health, psychological well-being, physiological functioning, and general functioning—but health behaviors were not influenced. Writing also increased immediate (pre- to postwriting) distress, which was unrelated to health outcomes. The relation between written emotional expression and health was moderated by a number of variables, including the use of college students as participants, gender, duration of the manipulation, publication status of the study, and specific writing content instructions.
Smyth, J. M. (1998). Written emotional expression: Effect sizes, outcome types, and moderating variables. Journal of Consulting and Clinical Psychology, 66(1), 174-184.
http://dx.doi.org/10.1037/0022-006X.66.1.174